Damping Behavior Of Mg/Al Laminated Sheets

Single pure Mg and pure Al sheets were fabriacted by rolling treatment，rollingtreatment was also performed on fabricating Al/Mg/Al sandwich laminated sheets, andaccumulative roll bonding （ARB） technique was used at room temperature by differentcycles to fabricate Mg/Al laminated sheets. Optical microscopy （OM） was used to testthe microstructure, the texture development of single Mg sheets was examined byEBSD （Electron back scattered diffraction）. The interface of the composite sheets wasinvestigated by SEM （Scanning electronic microstructure）. The mechanical propertiesof the plates are tested at ambient temperature, and dynamical mechanical analyzer（DMA） was used to investigate the damping capacity. In addition, different annealingtreatment was performed, discussing the effect of annealing temperature and time\on themicrostructure, interface and internal friction of composite sheets.For single Mg sheets, as the rolling deformation increasing, the grain size issmaller and at the same time, the yield strength and the tensile strength also inreased.However, the strain amplitude dependent internal friction （ADIF） was decreased as therolling reduction increasing, which due to the dislocation tangle increased. In thetemperature dependent internal friction （TDIF）, cast-Mg exist three internal frictionpeaks, but after rolled only one grain boundary relaxation peak can be clear seen inTDIF curves. However, when the rolled reduction arrived80%, there are two peaks, P2peak was the grain boundary relaxation peak, P3peak was the recrystallization. Fittingcalculation was worked on the P2peak of the rolled sheets and found this peak wasgrain boundary relaxation peak. The internal friction of pure as-rolled Al sheets was alsoinvestigated, the ADIF decreased with the decreasing of the thickness of Al sheets. TheTDIF of pure Al sheets exist two peaks, and the P2peak around300℃wasrecrystallization peaks.At room temperature, the Al sheets with different thickness were rolled with Mgsheets, the Al/Mg/Al Al/Mg/Al sheets was fabricated. The interface of Al/Mg/Al wasmechanical bonded, and the larger the rolling deformation of Al/Mg/Al sheets was, thethe interface bonded better. The mechanical properties and the damping capacity areaffected by the ratio of the thickness of Al layers in Al/Mg/Al sheets. For example, theratio of Al was higher in0.7Al/Mg/Al sheets and the rolling reduction is larger, so thestrength is higher. The ADIF of Al/Mg/Al was affected by the Mg layer, therefore, theADIF was decreased with the increasing of rolled reduction. The TDIF of Al/Mg/Alsheets exist two internal friction peaks, P1is relaxation peak and its activation energywas between the Mg and Al layer, P2peak is the recrystallization peak. After annealingat200℃, the interface bonding of Al/Mg/Al increased and exist obvious diffusion layer, otherwise, after annealing at250℃, there were three interface appeared, Al（Mg）/Al₃Mg₂，Al₃Mg₂/Al₁₂Mg₁₇, Al₁₂Mg₁₇/Mg（Al）. As the annealed temperature increasing,at low strain region, the ADIF decreased, but at high strain region, it increased quickly，which is connected with the growing of grain size. Annealed above200℃, the height ofP1peak in TDIF curves decreased, which was affected by Al layers, annealing at300℃which arrived the recrystallization temperature, so the height of P2peak decreasedobviously.Accumulative roll bonding technique was applied on sandwich sheets at roomtemperature by different rolling cycles, Mg/Al composite sheets exist straight interfaceand, except after rolling3cycles, localized necking appeared. While the rolling cyclesincreased, the ratio of the fine equiaxed grain increased and the uniformity of the grainincreased. Besides, the yield strength and the tensile strength also increased. However,the ADIF changes little when the rolled cycles increased. The TDIF of ARB-2cyclesheets exist three internal friction peaks, P1and P2are the relaxation peak, P3is therecrystallization peak. Compared with sandwich sheets, the interface bonding ofARB-3cycle sheets was better, therefore, after200℃annealed, the diffusion layer wasmore obvious, and after250℃annealed, there are also three interface. After annealed,the ADIF decreased, which may be affected by the impurity atoms diffusion in Mg layer,or the diffusion in Mg/Al interface. After annealed above200℃, the P2peak around200℃decrease obviously, which associated with the decreasing of the relaxation peakof the Al layers; the P1peak around150℃which connected with the grain boundaryrelaxation peak of the Mg layer; recrystallization occurred at250℃，so P3moved tohigher temperature and its height decreased.